Structure and stability of irradiation-induced Frenkel pairs in 3C-SiC using first principles calculations G. Lucas * , L. Pizzagalli Laboratoire de Me ´tallurgie Physique (UMR6630-CNRS), SP2MI, Bd Marie et Pierre Curie, BP 30179, 86962 Futuroscope-Chasseneuil Cedex, France Available online 21 December 2006 Abstract We have performed first principles calculations of intrinsic point defects and Frenkel pairs in cubic silicon carbide, using generalized gradient approximation. The considered Frenkel pairs have been obtained from a previous work on the determination of threshold dis- placement energies [G. Lucas, L. Pizzagalli, Phys. Rev. B 72 (2005) 161202]. Structures and formation energies of the defects are described. We found that our GGA results are in very good agreement with previous LDA studies. We found that Frenkel pairs are more stable than isolated single defects, especially for silicon interstitials, pointing to an attractive interaction between vacancies and interstitials as expected. Ó 2006 Elsevier B.V. All rights reserved. PACS: 68.55.Ln; 81.05.Je; 71.15.Mb Keywords: Silicon carbide; First principles calculations; Point defects; Irradiation 1. Introduction Silicon carbide is largely studied due to its possible use in eletronics, as a replacement for silicon in specific appli- cations, or in nuclear environments. In particular, there is a strong interest for understanding the behavior of silicon carbide under irradiation. Several mechanisms such as defects creation from cascades, amorphization, swelling, or crystal recovery are still actively investigated. A fun- damental quantity for describing damage creation in a material is the threshold displacement energy. Several theoretical works have been devoted to their determination in silicon carbide [1–6]. Recently, we have performed first principles molecular dynamics calculations for computing the displacement energies in 3C-SiC [7]. Several directions have been considered, each threshold energy being associ- ated with a specific Frenkel pair configuration. Due to the large number of runs and the long time associated with each molecular dynamics run, these simulations have been performed in small cells, encompassing 64 or 96 atoms. These limited sizes lead to a large uncertainty, about 1 eV, on the computed displacement energies. However, regarding the magnitude of the determined values, such an inaccuracy is more than acceptable. It is important to fully characterize the Frenkel pairs obtained during the determination of displacement ener- gies. In particular, interesting data are the structure and formation energy of the Frenkel pairs. The latter may be compared to single point defects energies, in order to gain information about crystal recovery. The aim of this paper is to describe and discuss the structure and stability of Frenkel pairs, obtained during displacement energy deter- minations [7], compared to single point defects. In this case, a 1 eV uncertainty is not acceptable and previously deter- mined Frenkel pairs have been relaxed in larger cells. Also, we used generalized gradient approximation (GGA) to investigate the effect of exchange correlation functional on the stability, since available studies in 3C-SiC are usu- ally performed within local density approximation (LDA). After a brief description of the method, we will first report the structure and the energies of intrinsic point 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.11.047 * Corresponding author. Tel.: +33 5 49 49 68 30; fax: +33 5 49 49 66 92. E-mail address: guillaume.lucas@etu.univ-poitiers.fr (G. Lucas). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 255 (2007) 124–129 NIM B Beam Interactions with Materials & Atoms